The invention relates generally to the field of fluid driven turbines, such as wind turbines or water turbines, wherein electrical power is generated from airflow across rotor blades. More particularly, the invention relates to blades for such turbines wherein the blades extend from a central rotating hub or shaft member to an annular rotating ring or rim member.
Fluid turbines such as wind turbines, also known as windmills, wind generators, wind machines or the like, and water turbines are well known devices for producing energy, typically electrical energy, by harnessing the power of moving fluids—either wind or water. Typical wind turbines used to generate large amounts of energy are very large structures, standing hundreds of feet tall and having rotor blades extending hundreds of feet, the rotor blades being mounted to a central hub or shaft. Large elongated blades are required since the area of blade sweep is proportional to the power that can be produced by a given wind turbine. This size creates a problem, in that each blade must act as a cantilever that can support the elongated blade and the blades must be increasingly massive toward the central hub in order to preclude the blade from breaking during use. Even with the use of high tech composites, carbon fibers and the like, a practical limit has been reached. For example, most large wind turbines have three blades, as this has been found to be the most efficient design. The desire to increase blade length in order to capture more wind is offset by the accompanying reduction in shaft revolutions per minute (rpm). Reduced rpm's require larger reduction gearboxes or larger diameter direct drive generators, both of which are undesirable. Decreasing blade pitch in order to increase the rpm's reduces torque, which is undesirable. In addition, repair or replacement of these giant blades or direct drive generators is difficult and can be extremely expensive. The cost of upkeep and repair reduces the overall benefits of energy production using wind technology. Thus, known wind turbine designs always have to make sacrifices in order to balance these competing factors. Many of these same problems and concerns befall water turbines that harness flowing water, tidal flows or ocean currents.
An alternative type of fluid turbine incorporates an outer, annular ring or rim that is joined to the blades, such that the blade tips are no longer self-supporting and thereby allowing the blades to be longer. The blades extend from the central rotating hub or shaft to the annular rim and are therefore supported at both ends. In this embodiment, it is also known to utilize the rotational energy from the rotating annular rim rather than the central hub, since the annular rim travels at much faster speed. Rollers, wheels, gears, magnets or the like are used to transfer the rotational energy from the rim to one or more generator mechanisms or the like. Examples of such turbines are shown in U.S. Pat. No. 4,319,865 to Richard, U.S. Pat. No. 4,330,714 to Smith, U.S. Pat. No. 4,350,895 to Cook, U.S. Pat. No. 4,545,729 to Storm, U.S. Pat. No. 4,729,716 to Schmidt, and U.S. Pat. No. 6,664,655 to Vann. Such turbines are often of smaller size and, for wind turbines, utilize sails rather than blades in order to increase the number of wind catching elements, since the weight of the annular rim adds structural problems to the design.
It is an object of this invention to provide a new blade construction for a fluid turbine having an annular outer rim that allows desirable structural characteristics to be maximized, such as increased blade length, increased blade durability, increased blade strength, increased blade number, reduced blade weight, lowered cost of materials, increased rpm, increased torque, reduced noise, variable control of blade pitch, and ease of replacement, among others. It is a further object to provide such a blade wherein the blades have sufficient strength such that the blades themselves provide the primary structural support for the annular outer rim of the turbine. Other objects not expressed will be apparent from the disclosure that follows.